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Installation details (low water pressure issue)

We've been considering a sprinkler system for our front, back, and side yards and thus, we've been gathering quotes. I have some inconsistencies that have concerned me so I'm hoping someone more knowledgeable here can help.

Our lot is large. Not including the house, the lot is about 6000 sq. ft. Our house sits in the middle of the lot so we have a huge backyard, a normal sized front yard, and two strips of yard on both sides of the house. We also have a kidney beaned shape of garden in the front.

We got quotes from 3 companies--all highly recommended by friends, realtor, etc. All are licensed as well.

Company one quoted us $2100. They said they were using Rainbird for 5 zones (only 5 zones for 2 side strips, a huge backyard, a front yard, and a garden area? seems like they under did the zones).

Company two quoted us $2500. They are using Hunter because we have low water pressure (40 psi) due to my rural city's crappy low water pressure at the city pump. They have 7 zones down.

Company three quoted us $4900. They are using Rainbird for 10 zones.

That $4900 seems like overkill. But am I wrong? Are sprinkler systems supposed to cost that much? Is any quote in the 2000 range a joke?

I did ask my neighbors about low water pressure. They all have 40psi as well and don't consider it "low." We do--the pressure inside and outside the house stinks. Our inspector (prior to closing) and our plumber have both commented that 40 is low. Normal is supposed to be 60-70 psi. The city says 40 is fine. Sounds to me like they need
more water pumps in the city to keep up with the growth and demand. How much will 40psi affect a sprinkler system?

Sorry for all the questions. My husband and I are brand new home owners and fairly not-Bob-Villa so any help we can get would be nice.

All I can say is 40 psi is a joke. No way will 5 zones cover your property. I highly doubt 7 zones will either. I would install some sprinklers above ground as a test. See how many sprinklers you can run. I've never seen a functioning sprinkler system with 40 psi unless it's a dripline.
Apparently they exist because your neighbors have them. Check out your neighbors sprinklers and see how many they have on one line. Compare it to what the three guys have in mind. Just remember that a full circle is 1 sprinkler. 2 half sprays is equal to 1 full. So if see 6 sprinklers at your neighbors on one line and they're half sprays. Don't expect you can run 6 full sprays in your yard.

With all that said keep in mind I'm not a landscape architect. I do however repair sprinkler systems full time. Working with systems that have very low pressure is a pain in the rear. In my opinion the more valves you have the better your odds of everything working correctly.

Even without the new Texas requirement (your local mileage may vary) about leaving trenches open for inspection, having a 40 psi supply pressure makes for an expensive sprinkler system. Every conceivable means to conserve water pressure gets utilized. No master valve, for instance (use zone valves with flow controls for operating reliability). Even then, heads won't throw as far as usual, so they get spaced closer together. Pipes may be oversized, because you want near-zero losses. Flows will be limited, according to your water supply pipe size and water meter size. This all costs money. Sometimes, it's so much extra money that boosting the pressure with a pump is considered.

Texas lawn sprinkling became a lot more expensive with their new rules. Anyone who does the work by the book is going to be significantly more expensive than some no-account trunk-slammer.

40 psi is extremely low for sprinklers

All of the companies who gave me quotes are licensed companies that have long histories (10+ years) of work in this area. None of them are "no-account-trunk-slammers." All of them claim to be following all of the new state laws (head to head coverage, permits and plans filed, freeze/rain sensor, etc.).
The problem is, I can't control a rural city's water pressure. The pressure is like this all over the city, yet over half the houses in it have sprinkler systems. Somebody must be doing something right.

All I can say is 40 psi is a joke. No way will 5 zones cover your property. I highly doubt 7 zones will either. I would install some sprinklers above ground as a test. See how many sprinklers you can run. I've never seen a functioning sprinkler system with 40 psi unless it's a dripline.
Apparently they exist because your neighbors have them. Check out your neighbors sprinklers and see how many they have on one line. Compare it to what the three guys have in mind. Just remember that a full circle is 1 sprinkler. 2 half sprays is equal to 1 full. So if see 6 sprinklers at your neighbors on one line and they're half sprays. Don't expect you can run 6 full sprays in your yard.
With all that said keep in mind I'm not a landscape architect. I do however repair sprinkler systems full time. Working with systems that have very low pressure is a pain in the rear. In my opinion the more valves you have the better your odds of everything working correctly.

Everybody in my HOA who has a sprinkler system, has 30-50 psi, so obviously it is possible. We are planning to go talk to neighbors--good advice there. I'm hoping we can figure out what kind of systems they have that work. The quote with 7 zones is on par with my neighbors. Most of them have 6-7 zones, with about 70-100 heads.

Even without the new Texas requirement (your local mileage may vary) about leaving trenches open for inspection, having a 40 psi supply pressure makes for an expensive sprinkler system. Every conceivable means to conserve water pressure gets utilized. No master valve, for instance (use zone valves with flow controls for operating reliability). Even then, heads won't throw as far as usual, so they get spaced closer together. Pipes may be oversized, because you want near-zero losses. Flows will be limited, according to your water supply pipe size and water meter size. This all costs money. Sometimes, it's so much extra money that boosting the pressure with a pump is considered.

Is the pressure boosting pump something that is part of the sprinkler system, or is that something that would be installed at the city line to boost pressure for the entire lot?
If it were one company quoting way under, I'd be concerned. But I have three companies--all with bids in the $2000 range and one with a bid of $4900. It just makes the $4900 look way over priced and like over kill.

There is a tremendous difference between 40 psi and 50 psi, when it comes to a supply pressure you can work with. If your pressure is subject to fluctuation, then different companies might be seeing a different picture, depending on when they measured pressure. (I myself, encountered an extreme example of this, and submitted a design and bid that was more than double anyone else's, on account of having measured a supply pressure less than half of what was usually present)

Since Texas has curbside meters, an installer can minimize pressure losses, unlike other states in the north, where meters are in basements, and pressure gets lost in the pipe supplying the home.

There is a tremendous difference between 40 psi and 50 psi, when it comes to a supply pressure you can work with. If your pressure is subject to fluctuation, then different companies might be seeing a different picture, depending on when they measured pressure. (I myself, encountered an extreme example of this, and submitted a design and bid that was more than double anyone else's, on account of having measured a supply pressure less than half of what was usually present)

Since Texas has curbside meters, an installer can minimize pressure losses, unlike other states in the north, where meters are in basements, and pressure gets lost in the pipe supplying the home.

I had the city out today. We're 2 miles from the water tower, downhill no less. My neighbors are all getting 50-60 psi. They measured me today, at noon (when everyone is not using their water much) and we were at 42psi. They said they can't guarantee more than that and tried to hand wave me. I told them they would be providing me with the same water pressure as my neighbors or they'd be paying for my sprinkler system. So now they are going to monitor our pressure for a bit and see what's what.

I have to agree with the other posts. 40 PSI static is very low for a sprinkler system. Most rotary sprinkler heads operate at their optimum
at the 45-50 psi range. You're starting out with 42 PSI. By the time you figure all your pressure losses in the service line, meter, backflow device, valves, piping, elevation, etc. etc. you could very well be operating at best in the low 30's but likley in the 20's. You might want to inquire with the three contractors what they figure the pressure is going to be at the base of the heads for the worst zone. A booster pump is looking good for this application. I doubt you will have much success any other way. Where did you come up wth 70-100 heads on seven zones with 30-50 PSI?

If all you can count on is 42 psi, then you deal with it. Pipe sizes are bumped up. If there was going to be a master valve, that could be eliminated, getting you back about 3 psi. If you already have a one-inch water meter, then you can't do anything there. Flow losses in a one-inch meter should be less than 3 psi, if your flow is less than 20 psi.

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You still have the losses of a backflow preventer and a zone valve. 3 psi here, 5 psi there, and it adds up pretty quick. In your best scenario, you will be lucky to have as much as 30 psi at the sprinkler heads. The best designs will be very conservative. Better to have 10 zones that work, than to have 5 zones that don't.

I have to agree with the other posts. 40 PSI static is very low for a sprinkler system. Most rotary sprinkler heads operate at their optimum
at the 45-50 psi range. You're starting out with 42 PSI. By the time you figure all your pressure losses in the service line, meter, backflow device, valves, piping, elevation, etc. etc. you could very well be operating at best in the low 30's but likley in the 20's. You might want to inquire with the three contractors what they figure the pressure is going to be at the base of the heads for the worst zone. A booster pump is looking good for this application. I doubt you will have much success any other way. Where did you come up wth 70-100 heads on seven zones with 30-50 PSI?

The 70-100 heads with 7 zones on the 30-50 psi is what some of my neighbors say they have (ones who just had systems installed recently). I did find out that my neighbors are mostly staying in the 45-55 psi zone where I am not. At the street level, I'm averaging between 28-42, a fluctuation that the city says shouldn't be happening. My response--Gee, really? So fix it!

If all you can count on is 42 psi, then you deal with it. Pipe sizes are bumped up. If there was going to be a master valve, that could be eliminated, getting you back about 3 psi. If you already have a one-inch water meter, then you can't do anything there. Flow losses in a one-inch meter should be less than 3 psi, if your flow is less than 20 psi.

You still have the losses of a backflow preventer and a zone valve. 3 psi here, 5 psi there, and it adds up pretty quick. In your best scenario, you will be lucky to have as much as 30 psi at the sprinkler heads. The best designs will be very conservative. Better to have 10 zones that work, than to have 5 zones that don't.

The $4900 quote means we won't get a system. We can't afford that so it would be a year or two before we looked at a system. During which, we're stuck hand watering a monster lot or using hose sprinklers that just aren't getting everything. The 7 zone $2600 price is something we can do. There is not a single person on my street with 10 zones. They are all 6-7 zones. Their systems have no problems so I know it is possible.

I know what you are saying. But I also have to look at what I can afford as well.